I know that Tableau Prep Builder is a relatively new product and it would help a lot if the error handling was a bit better.
Sometimes the messages do not provide much information and refer to log files for more details. It would make it easier for the end-user to find out what is causing the issue if there was a link to the mentioned log. The process of going through logs for someone without experience is a lot in itself and trying to figure out which log they should look at in the first place makes the task almost impossible. That's why including a link in the error message, or at least the name of the file would be of great help.
(screenshot of reference)